Crop harvesters or mowers are typically provided with sickle assemblies which include a reciprocating sickle provided with generally triangular-shaped knife sections and suitable stationary, pointed guards which are typically slotted to receive the horizontally moving sickle. The guards serve the dual purpose of providing co-acting shear surfaces for the knife sections and protection against breakage of the sickle from rocks and other obstructions encountered in the field.
Although it is fairly standard for such guards to have points or fingers which are simply slotted to receive and confine the reciprocating sickle, in certain fine, light grass situations it has been found that a different type of guard is more effective than the standard slotted variety. In this respect, the assignee of the present invention has for many years manufactured and sold so-called "stub" guards in which the upper and lower halves of the guard are two separate pieces so that the gap or slot in which the sickle reciprocates is open at the tips of the guards instead of being closed as in the standard, slotted guards. Consequently, it is possible to have the knife sections project slightly through and beyond the guard tips during reciprocation and thereby effect a self-cleaning action within the gap. Without this action, and using the standard, slotted guard, there is a tendency for the slender grass stems to hairpin over the edge of the gap instead of becoming fully severed and to thus collect and clog up the gap area. Eventually, this prevents the knife sections from properly entering the gap and, instead, causes them to deflect upwardly or downwardly to impact with the sides of the guards and shatter. Replacement of the knife sections is a tedious and time-consuming operation which is particularly frustrating at harvest when time is at a premium.
The open-ended sickle gap of prior stub guards is thus quite beneficial and yet the size of the gap itself is critical insofar as proper cutting action is concerned. In this respect, it will be appreciated that the knife sections are subjected to irregular yet significant upward loading forces as the sections engage and sever the standing crops. Thus, there is a tendency for the sections to deflect upwardly unless restrained by the overlying upper fingers of the guards. If such deflection and upward movement is too great, the proper cooperative shearing action between the knife sections and the upper ledger surface of the bottom guard fingers will not take place; hence the grass stems will simply hairpin over the edges of tee lower guard fingers and be shoved into the gap by the knife sections instead of being severed in the intended manner. This, then, results in the knife breakage problem as mentioned above.
Heretofore, in order to adjust the size of the gap on stub guards, it has been necessary to place an appropriate number of shims between the upper and lower fingers so that when the fingers were bolted down together on the cutter bar, the size of the stack of shims would determine the spacing between the fingers and thus the size of the gap. Manifestly, adding more shims or taking others away as necessary along the twelve-to fourteen- foot length of the sickle assembly comprises a tedious, time-consuming task made all the more frustrating and bothersome by the fact that the bolts and other loose components are easily lost and misplaced after disassembling the guard each time a shim is to be added or removed. This itself, therefore, discourages proper adjustment of the gap and simply exacerbates the poor cutting and excessive sickle breakage problem.